Now that I know I can't drink water, all I think about is drinking water.
I'm not supposed to drink any water until tomorrow morning, so I can't stop thinking about it.
この場合、次のように言うと良いですよ。
ーNow that I know I can't drink water, all I think about is drinking water.
「水を飲めないと思うと、水を飲むことばかり考えてしまう」
all I think about is ... で「…ばかり考えてしまう」
ーI'm not supposed to drink any water until tomorrow morning, so I can't stop thinking about it.
「明日の朝まで水を飲んだらいけないので、水を飲むことが頭から離れない」
I can't stop thinking about it. で「そのことばかり考えてしまう・そのことが頭から離れない」
ご参考まで！
"As soon as I think that I can't drink water, all I can think about it drinking water."
"As soon as I think that I can't drink water, all I can think about is drinking water."
"as soon as I think that ~" 「〜と思った途端」
"I can't drink water" 「水を飲めない」
"All I can think about is ~" 「〜ばかり考えてしまう」
"drinking water" 「水を飲むこと」
[ばかり考えてしまう](https://eikaiwa.dmm.com/uknow/questions/13579/)についてもっと詳しく知りたい方はクリックしてください。
カナダ 
オーストラリア 
